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Date: Wed, 20 Sep 2000 15:50:36 -0700 (PDT)
From: earl_chew@agilent.com
To: freebsd-gnats-submit@FreeBSD.org
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Subject: gnu/21433: g++ optimiser produces bad code on right shift of 64 bit integer
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>Number:         21433
>Category:       gnu
>Synopsis:       g++ optimiser produces bad code on right shift of 64 bit integer
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Sep 20 16:00:01 PDT 2000
>Closed-Date:
>Last-Modified:
>Originator:     Earl Chew
>Release:        4.0-RELEASE
>Organization:
Agilent Technologies
>Environment:
FreeBSD bna2188.canada.agilent.com 4.0-RELEASE FreeBSD 4.0-RELEASE #0: Mon Mar 2
0 22:50:22 GMT 2000     root@monster.cdrom.com:/usr/src/sys/compile/GENERIC  i38
6
>Description:
The attached test harness fragment dealing with >> on 64 bit integers
fails when optimisation is enabled.

The program works when no optimisation is used.

Compile with g++ -O foo.cc. Running the program yields:

0x8888222233334444 0
0x8888222233334444 0xffffffff33334444
Failed: Signed negative right shift identity operation

>How-To-Repeat:
#include <stdio.h>

typedef unsigned long long AtoUInt64T;
typedef long long AtoInt64T;

typedef AtoUInt64T U;
typedef AtoInt64T S;

int main()
{
    do
    {
        S  r ((AtoUInt64T) ( 0x88882222UL ) << 32 |
              (AtoUInt64T) ( 0x33334444UL )) ;
        S  a ((AtoUInt64T) ( 0x88882222UL ) << 32 |
             (AtoUInt64T) ( 0x33334444UL )) ;

        int  b = 0x0+0x00 ;
        S  c;

        c = a >> b;

        if (c != r)
        {
            printf("0x%llx %d\n", a, b);
            printf("0x%llx 0x%llx\n", r, c);
            printf("Failed: %s\n",
                "Signed negative right shift identity operation" );
            abort();
        }
    } while (0) ;

    return 0;
}

>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted:


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